Regarding close portraiture: I would probably prefer 150mm to 200mm. I have 100mm, which I use with 1.4 tele converter to make it roughly 140mm. With converter I loose 1 stop in aperture, but can gain a closer look because 100+1.4 converter focuses relatively close to the subject. It works. I have got 200mm also wich I would use with extension tubes to get closer to the subject. This is more classic setup for GS-1 for this type of portraits. Now what makes the difference is the extent of distortion. I think you should see it by yourself and judge after, if possible. For me, the compression I get with 200+extension tube is too much, the face is really flattened. People can like it, but for me it is too much. So, considering that both 150 or 200 will need something to get camera closer to the subject, probably the tube, one should (by my opinion) decide by estetical goals like a distortion.
When I look at the portrait posted by Howard, I would say, the same person would look very different with 200mm. I like his example and I would not use for this particular subject anything longer that 150mm.